Injection devices for setting and dispensing a single or multiple doses of a liquid medicament are as such well-known in the art. Generally, such devices have substantially a similar purpose as that of an ordinary syringe.
Injection devices, in particular pen-type injectors have to meet a number of user-specific requirements. For instance, with patient's suffering chronic diseases, such like diabetes, the patient may be physically infirm and may also have impaired vision. Suitable injection devices especially intended for home medication therefore need to be robust in construction and should be easy to use. Furthermore, manipulation and general handling of the device and its components should be intelligible and easy understandable. Moreover, a dose setting as well as a dose dispensing procedure must be easy to operate and has to be unambiguous.
Typically, such devices comprise a housing including a particular cartridge holder, adapted to receive a cartridge at least partially filled with the medicament to be dispensed. Such devices further comprise a drive mechanism, usually having a displaceable piston rod which is adapted to operably engage with a piston of the cartridge. By means of the drive mechanism and its piston rod, the piston of the cartridge is displaceable in a distal direction or dispensing direction and may therefore expel a predefined amount of the medicament via a piercing assembly, which is to be releasably coupled with a distal end section of the housing of the injection device.
The medicament to be dispensed by the injection device is provided and contained in a multi-dose cartridge. Such cartridges typically comprise a vitreous barrel sealed in distal direction by means of a pierceable seal and being further sealed in proximal direction by the piston. With reusable injection devices an empty cartridge is replaceable by a new one. In contrast to that, injection devices of disposable type are to be discarded when the medicament in the cartridge has been dispensed or used-up.
Existing and commercially distributed pen-injectors may be equipped with cartridges providing a predefined volume for a liquid medicament, e.g. 3 ml. The injection devices are typically configured to provide user-operated variable setting of a dose and subsequent dispensing or delivery thereof. Typically, a dose can be selected and dispensed in discreet steps of e.g. one or several International Units (IU). Most injection devices on the market are configured and designed for use of grown up patients.
In the field of pediatric treatment it is desirable to reduce the dose of medicaments and to administer non-integer amounts of IU to a patient. This requires smaller dose increments to be selectable. It is therefore desirable to set and to dispense doses having a size of less than one IU, e.g. of half units. Hence, it is desirable to provide dose setting with increments of half units or less in order to increase dosing accuracy and to allow for a finely segmented, precise setting and dispensing of doses of a particularly small size.
In order to meet these requirements existing injection devices require modifications.